Safety system for luminescent tubes



July 7, 1953 n. c. HULTGREN SAFETY -sysm Fon Vrml'mzscxan'r 'rusas meaJune v. 194') Patented July 7, 1953 SAFETY SYSTEM FOR LUMINESCENT TUBESlRudolph C. Hultgren, Chicago, Ill., assignor, by mesne assignments, toBert C.- Pretzer, Detroit, Mich., and Rudolph C. Hultgren, Chicago,Ill.,

jointly Application June 7, 1947, Serial No. 753,246

The present invention relates to systems and circuits for the operationof luminescent electric tubes, and constitutes an improvement upon theconstruction described and claimed in my copending application, SerialNo. 587,945, led April 12, 1945, now abandoned.

Operating potentials, in the neighborhood of 600 volts, required forcertain cold-cathodelighting tubes are regarded as unsafe and `my priorapplication discloses a safety fixture and system for protecting personsfrom. the high voltage conductors. It is desirable for improved economyof installation and operation to employ two tubes in series, but thehigher circuit voltage required for such series operation has,understandably, been regarded as even more dangerous.

One object of the present invention is the provision of an improvedsystem in which the haz-` ards of such a series system are no greaterthan those of the shunt system.

Another object is the provision of a safety control :for such a seriessystem so that persons will be effectively protected from contact withenergized high voltage conductors.

A further object is the provision ofl an improved cold-cathode,luminescent-tube system, and the provision of an improved safety controlfor such systems.

In the preferred embodiment of my invention, the ballast transformer hasa separate, insulated secondary winding for each series pair ofluminescent tubes. and the connection between the two tubes, that is themid-point of the load, is connected to the primary circuit. Furthermore,this connection to the primary is accomplished by a circuit controllingsocket that interrupts the primary to deenergize the transformerwhenever a tube is removed. s

These and other objects and advantages will appear from the followingdescription of a specilic construction which illustrates the manner inwhich the invention may be carried out.

In the drawings:

Fig. l is a view, partly in section of a lighting fixture andluminescent tubes therein;

Fig. 2 is a schematic diagram showing the luminescent-tube circuit of mypresent invention; and

Fig. 3 shows a modification of the circuit of Fig.2.

In Fig. l a housing lll contains an insulating plate l2 which supportsfour helical spring sockets I4. A second housing 'I6 contains aninsulator I8 which supports four split-cone 3 Claims. (Cl. 315-187) 2sockets 2l) of the type shown in my application, Serial No. 743,248,iiled April 23, 1947, now abandoned. The sockets I4 and 20 are adaptedto receive and hold luminescent tubes 22. A tube is rst inserted throughan yopening 24 in housing ID into a socket I4, and forced into thesocket to distend it enough that the other end of the tube'22 may beinserted through a similar opening 26 in housing I6 into a socket 20,Where it is firmly seated by the force of the spring of socket i4. Metalterminal caps 28 on the tubes 22 provide the electrical connections ofthe tubes to the sockets I4. A similar cap 38 on the other end of eachtube bridges the two halves of its socket 20. These split-cone socketsconstitute switches and are connected in series by straps 32s@ that thecircuit is complete only when the tube-caps 30 are seated in all four ofthe sockets, as is described in said application, Serial No. 743,248.

The tubes 22 areoiv the cold-cathode, instantaneously-starting type,operating with about 450 volts R. M. S. drop across the tube butrequiring a somewhat higher total circuit voltage, the difference beingabsorbed in a reactance.

In Fig. 2, the four tubes 22 are shown schematically in my improvedcircuit. A transformer 40 includes a primary winding 42 and two-similarsecondary windings 44 and 46 insulated ircmthe primary winding and eachof which has considerable self ,inductance to provide the ballast neededfor limiting the current tothe tubes 22. Any number of such secondarywindings may be used. The secondary windings may have additionalinductive or capacitive ballast devices connected in series with them asis well known in the art. Thus, a condenser 48 in series with Winding 44provides ballast and improves the power factor of the current drawn bythe primary winding. This winding 44 supplies a loadconsisting of twotubes 22 which at their ends remote from winding 44 (their right ends asviewed in Fig. 2) are connected to the primary circuit. Thus, althoughWinding 44 may 'deliver a total of about 900 volts under load, onlyabout half of that can appear between either' left-hand tube terminal 28and ground because one conductor of the volt input will be at or nearground potential. Furthermore,

should one tube fail to operate the other one will be thereby preventedfrom operating, and under such condition, winding 44 will be eiectivelyisolated by the extremely high resistances of the unlit tube. lNot onlydoes the socket constructon'of Fig. 1 prevent contact with the concuitis opened and the secondary windingsde-` energized. Consequently it isimpossible for a person t come into contact with highv voltage when atube is removed unlesssocket 21V-is tampered with, as by the insertioncfa-conductor therein. But even in that case that person can receive thehigh voltage only throughav circuit l that includes the other tube. Inthis respect, the present series system is even more safe than the shuntsystem of my prior application, Serial No. 587,945, previouslyV referredto, which. employs a lower secondary voltage at the` trans.-` former.

In the circuit modification of Fig. 3, an impedance elcment'orcondenserv ll'isconnected froml ground `52' to'a part of winding 44inter-- mediate the terminals thereof, such as the mid-- voltage point,the core 43A of the transformer being also grounded as indicated"at"54.Alternatively, condenser Slmay be connected between said winding 44yandone of the terminals of primary winding 42: Condenser''hasanimpedance, atthe frequency of the supply voltage, which is highcompared to that'of the tubes 22 when they are operating, but lowcompared to that of those. same tubes when unlit. Accordingly, whenthetubes are unlit, thefpath through condenser Ell-will effectively tiethe mid-voltage point of the winding to ground andso prevent the fullvoltage of the winding from appearing between either socket I4 and"ground when'one tube is defective or when a tube is removed vand itssocket 'is tampered'with' for closing the primary circuit. When thetubes are lit, condenser 50? will be a high impedance shuntto aA part ofthe circuit and so have little effect.

The circuit of Fig. 2` hasy the advantage: that the winding 44 is betterisolated from the other windings.

Thus the present invention provides thesafety of the shunt system but aneconomy; of the iseries system. Two tubes in series will strike atvlessthan twice the voltage required for two tubes, because the voltage willnot initiallyy divide equally between the two tubes so that'they lightin turn. Thustwo tubes requiring '750 volts'for shunt operation may beoperated in series on 1300 volts. In addition, with the circuit of Fig.3, the primary voltage is added to that of one of the two tubes foraiding its starting. After that one tube starts, its impedance drops toincrease the voltage appliedto the other so that it starts too.

While I have shown and particularly described' a preferred embodiment ofmy invention, the specific features thereof, and the-detailedexplanationy should not be construed as limiting except as requiredbythe claims.

What` I claim as new and desire-to protect by Letters Patent of theUnited Statesis:

1. Alsystem for energizing a pair ofluminescent electric tubes from analternating current power supplycomprising, a transformer including aprimary winding and a secondary Winding separate, andv conductivelyisolated, therefrom, means for connecting the primary winding to thealternating current power supply, means for connecting the pair ofluminescent electric tubes in series with each other and in series withthe secondary winding only of said transformer including means forconnecting one end of'one tube to one endy of the secondary winding andincluding a condenser in series, means for connecting one end of theother tube tothe other end of the secondary winding and meansforconnecting the other ends of the tubes together, said means forconnecting the primarywinding'to the alternating current supply',lincludingsaid means for connecting the other endsof the tubes togetherso that the connection between said other ends of the tubes isat.no.time Ahigher than the potential of the alternating current power supplyto the primary winding and so that when the connection between saidother ends of the tubes is broken, theiconnection between the primarywinding and the alternating current power supply is also broken;

2. A system for energizing a pair of luminescent electric tubes from analternating current power supply comprising, a transformer including'aprimaryy winding and a secondary winding separate and` conductivelyisolated therefrom, means for connecting the primary winding' to thealternating current power supply, means including a condenser forconnecting the center of the secondary winding to ground, meansfor-connecting the pair of luminescent electric tubes in series witheach other and in series with the secondary winding only of saidtransformer including means for connecting one end of one tube to oneend of the secondary winding and including a condenser in series,means-for` connecting one end of the other tube to the other end of thesecondary winding and means for connecting the other ends of the tubestogether, said means for connecting the primary windingl to thealternating current supply including said means for connecting the otherends of the tubes together so that the connection between said otherends of the tubes is at no time higher than the potential 'of thealternating currentpower supply to the primary winding and so that whenthe connection between said other endsfof ,the tubes is broken, theconnection between the primary winding and the alternating current powersupply is also broken.

3. vAv system for energizing a plurality of pairs of luminescentelectric tubes from an alternatingcurrent power supply comprising, atransformer including a primary winding and a plurality of secondarywindings separate and conductively isolated therefrom, one secondarywinding being provided for each pair of luminescent electric, tubes,means for connecting the primary Winding to the alternating currentpower supply, a plurality of connecting means each comprising means forconnecting the luminescent electric tubes of each pair in series witheach other and in series'with its associated secondary winding only ofsaid transformer including meanszfor connectingv one end of one tubetoone end of the secondary winding, means for connecting one end of theother tube to the other end of the secondary winding and means forconnecting the other ends of the tubes together, said-,means forconnecting the primary winding` to-the alternating current supplyincluding. all ofY said means for connecting the other. ends ofthe tubestogether so that all of said connections between said other ends of theNumber Name Date tubes are at no time higher than the potential1,950,396 Boucher Mar. 13, 1934 of the alternating current power supplyto the 1,954,557 Comstock Apr. 10, 1934 primary Winding and so that whenany of said 2,295,757 Russell Sept. 15, 1942 connections between saidother ends of the tubes 5 2,305,096 McDermott Dec. 15, 1942 are broken,the connection between the primary 2,317,845 Boucher Apr. 2'7, 1943winding and the alternating current power sup- 2,401,555 De Reamer June4, 1946 ply is also broken. 2,402,207 Ranney June 18, 1946 OTHERREFERENCES Referencs Cited in the me of this patent Standard Handbookfor Electrical Engineers, UNITED STATES PATENTS 7th edition, 1941(McGraw-Hill, New York), Number Name Date page 1332 (sec. 14-68); copyin Sci. Library.

1,689,485 Hendry Oct. 30, 1928 15

